A frequency modulation apparatus capable of reducing a peak level of a radiation noise of a characteristic frequency band due to an image clock.This frequency modulation apparatus is used in an image formation apparatus having an image bearing body to be scanned by a laser beam, and comprises an auxiliary clock calculating portion for calculating an auxiliary clock period based on a reference clock period and a modulation coefficient, and an image clock generating portion for generating the image clock in which a frequency is different at least in one portion and other portions of an image area on a main scan line to be scanned by the laser beam on said image bearing body based on the initial period value set in advance and said auxiliary clock period, and said image clock generating means perform a frequency modulation so that the frequency of said image clock changes within a predetermined fluctuation.